An especially popular type of active matrix display is an active matrix liquid crystal display ("AMLCD") formed by confining a thin layer of liquid crystal material between a front plate having a front electrode, and a back plate having a matrix of back electrodes. The front plate typically comprises a transparent material such as glass, and the back plate typically comprises a glass substrate with processed thin-film or amorphous silicon transistors for transmissive type AMLCDs, or a silicon substrate with processed MOS transistors for reflective type AMLCDs. Pixels are defined by the front and back electrodes so as to be optically responsive to voltages applied across liquid crystal material residing between the front and back electrodes.
In conventional AMLCDs, although the voltage applied to the front electrode is not necessarily restricted in magnitude since it may readily be generated as an analog signal, the voltages applied to the back electrodes commonly are restricted for convenience in their generation, to logic level voltages such as the 5.0 volts commonly used by digital circuitry. In certain applications, however, such a restricted voltage may result in compromising the performance of the AMLCD. For examples, it may preclude the use of certain liquid crystal materials such as electroclinic liquid crystal materials, which require high voltages for proper operation, or it may limit the range or application of certain other liquid crystal materials such as nematic liquid crystal material, wherein a high voltage range is desirable for high resolution gray scale applications.